Car engine mechanism

The process by which a car works is a lot simpler than you may think. When a driver turns a key in the ignition:

The car battery powers up sending

Power to the starter motor, which

Turns the crankshaft, which

Gets the pistons moving

With the pistons moving the engine fires up and ticks over

A fan draws air into the engine via an air filter

The air filter removes dirt and grit from the air

The cleaned air is drawn into a chamber where fuel (petrol or diesel) is added

This fuel-air mix (a vaporised gas) is stored in the chamber

The driver presses the accelerator pedal

The throttle valve is opened

The gas-air mix passes through an intake manifold and is distributed, through intake valves, into the cylinders. The camshaft controls the opening and closing of the valves.

The distributor makes the spark plugs spark, which ignites the fuel-air mix. The resulting explosion forces a piston to move down which in turn causes the crankshaft to rotate.

What happens in the cylinders is the magic that gives power and motion to the car wheels. Most car engines use a four-stroke combustion cycle. This cycle starts with piston at the top of the cylinder. Then:

Inside A Car Cylinder

Four Stroke Combustion Cycle

Intake stroke: intake valve opens and the piston moves down allowing the fuel-air mix to enter the open space.

Compression stroke: the piston moves upwards. This compresses the fuel-air mix by forcing it into a smaller space. Compression makes the fuel-air mix explode with greater force.

Power cycle: spark from a spark plug ignites the fuel-air mix. The explosion forces the piston down the cylinder.

Exhaust cycle: the exhaust valve opens and the piston moves back to the top of the cylinder which forces the exhaust fumes out.

The bottom of each piston is attached to the crankshaft.

As the pistons are forced up and down they rotate the crankshaft, which after sending the power through the transmission, turns wheels.

Most cars have at least four cylinders. More powerful cars have more. For example a V6 has six cylinders and a V8 has eight.

The harder a driver presses on the accelerator pedal the more fuel-air mix is passed into the cylinders and the more power is produced.

What Are Revolutions Per Minute?
The four-stroke cycle repeats itself thousand of times a minute. These repetitions are more commonly known as Revs.

A rev counter tells you how many thousand times per minute the cycle is repeated.

The Transmission

Controls the power contained in the crankshaft before it goes to the wheels and allows a driver to control the speed/power of a car by providing different speed/power ratios known as gears.

So first gear gives plenty of power but little speed whereas fifth gear provides little power but plenty of speed.

The crankshaft only connects to the transmission when the car is in gear and the clutch is engaged. If you press down on the clutch the crankshaft disconnects from the transmission.

The transmission is connected to the output shaft, which is connected to the axles, which are connected to the wheels. When the transmission rotates the output shaft this turns the axles, which in turn rotate the wheels.

Alternator: turns mechanical energy into electrical energy. This energy powers a car's electrics, from lights to wipers. It also recharges the car battery. A belt that rotates once the engine is on powers it.

Brakes: cars use either drum or disc brakes. Disc brakes use a calliper to press onto the disc of the wheel in order to slow the wheel down. Drum brakes work on the same principle however a drum brake presses against the inside of the drum.

Camshaft: controls the opening and closing of the intake and exhaust valves.

Cooling System: car engines produce a lot of heat. This heat needs to be controlled. To do this water is pumped through passages that surround the cylinders and then through the radiators to cool down.

Distributor: operates the ignition coil making it spark at exactly the right moment. It also distributes the spark to the right cylinder and at the right time. If the timing is off by a fraction then the engine won't run properly.

Exhaust System: once the fuel-air mix has been burnt the remaining gas enters the exhaust system and is expelled from the car. If a catalytic converter is present the exhaust gas passes through it and any unused fuel and other certain chemicals are removed.

Handbrake: this is a separate system from the foot brake. As a rule it is mounted on the floor of the car and is connected by a cable to the two rear wheels.

Source: www.driving-test-success.com

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